A conventional plate type speaker will be described with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view of a conventional plate type speaker, and FIG. 2 is an exploded perspective view of a coupling structure of a voice coil, permanent magnets and plates employed in the conventional plate type speaker.
As shown in FIGS. 1 and 2, a flat coil plate 36 with a top end to which a flat diaphragm 30 is vertically fixed is inserted into an assembly of upper plates 31a, 31b, 31c, 31d, 32a, 32b, 32c and 32d, lower plates 33a, 33b, 33c, 33d, 34a, 34b, 34c and 34d and permanent magnets 37 fixed therebetween. The assembly of permanent magnets and upper and lower plates is fixed to a base frame 35. Then, an edge 39 is bonded to the periphery of the flat diaphragm 30 and secured by a guide ring.
An electric current generated at a speaker driving circuit is supplied to a voice coil 38 fixed at the coil plate 36 to produce a magnetic field at the voice coil 38. The magnetic field cooperates with a facing magnetic field generated from the polarity of the permanent magnet-plate assembly, thereby generating a force that vibrates the coil plate 36 and the flat diaphragm 30 fixed thereto. Consequently, the vibration of the diaphragm 30 causes sound to radiate outside.
At this time, the coil plate 36 is kept in non-contact with the upper and lower plates 31 to 34 not to interfere with the vibration of the planar diaphragm 30 and is connected to the permanent magnets 37 as close as possible so that the coil plate can be much influenced by the magnetic field.
However, in the conventional plate type speaker constructed as above, there is difficulty in manufacturing the plate type speaker in that the coil plate 36 should be bent according to the shapes of spaces between the upper plates 31 and 32 and between the lower plates 33 and 34.
Further, if the coupling direction or shape of the coil plate 36 is changed due to long-time use of the speaker, there is a problem in that the coil plate 36 comes into contact with the upper and lower plates 31 to 34, resulting in abnormal vibration of the diaphragm 30.